In accordance with recent trends for miniaturizing and making electric and electronic machinery and tools having a high performance, a material for components used therein, such as a connector, has been required to be further improved in all the features.
For example, a spring sheet used at a contact point of a connector has been modified to become thinner and thinner, which becomes difficult to keep a sufficient contact pressure. That is, when the spring sheet is deflected at a contact point of the connector, a counterforce is generated to give a contact pressure to make electrical connection. Therefore, the thinner the sheet is made, the larger the sheet has to be deflected to keep a contact pressure at a similar level. However, when the sheet is deflected to the extent exceeding an elasticity limit of the sheet, plastic deformation is occurred. Accordingly, additional improvement is demanded to prevent plastic deformation.
It is also demanded to improve the spring sheet in various features including stress relaxation property, heat conductivity, bending property, heat resistance, plate adhesion property, and migration resistant property. Among the properties, mechanical strength, stress relaxation, heat and electric conductivity, and bending property are important, when the material is used at a contact point of the connector.
Conventionally, phosphor bronze has been used at the contact point of the connector. However, it cannot be perfectly satisfied with the demands as described above. Accordingly, phosphor bronze recently has been replaced by a beryllium-copper alloy, that is an alloy prescribed in JIS C 1753. Such a beryllium-copper alloy has an improved mechanical strength and a good stress relaxation property, as well as a good electric conductivity. However, the beryllium-copper alloy is very expensive, and beryllium is toxic.
For these reasons, it is demanded to develop an alloy, which is inexpensive and nontoxic, and which is comparable to the beryllium-copper alloy. One of studies has been focused on a Cu—Ni—Si alloy since around 1985, since it has a high mechanical strength.
However, any of the Cu—Ni—Si alloys developed cannot be an alternative of the beryllium-copper alloy, since they are inferior in mechanical strength and stress relaxation resistance compared with the beryllium-copper alloy.
Besides, addition of Mg into a Cu—Ni—Si alloy has been proposed to improve a stress relaxation property. Addition of Mg improves stress relaxation resistance to some extent, but an improvement of the stress relaxation resistance in the level of beryllium-copper alloy has not been accomplished.